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Revision History for A141113

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A141113

Positive integers k such that d(d(k)) divides k, where d(k) is the number of divisors of k.
(history; published version)

#17 by Bruno Berselli at Tue Feb 19 04:42:23 EST 2019

STATUS

reviewed

approved

#16 by Michel Marcus at Tue Feb 19 04:38:16 EST 2019

STATUS

proposed

reviewed

#15 by Jinyuan Wang at Tue Feb 19 04:24:27 EST 2019

STATUS

editing

proposed

#14 by Jinyuan Wang at Tue Feb 19 04:24:14 EST 2019

LINKS

Jinyuan Wang, <a href="/A141113/b141113.txt">Table of n, a(n) for n = 1..10000</a>

PROG

(PARI) is(k) = k%numdiv(numdiv(k)) == 0; \\ Jinyuan Wang, Feb 19 2019

CROSSREFS

Cf. A000005 (tau), A010553, A141114, A141115.

STATUS

reviewed

editing

#13 by Michel Marcus at Tue Feb 19 04:09:50 EST 2019

STATUS

proposed

reviewed

#12 by Jon E. Schoenfield at Tue Feb 19 04:07:12 EST 2019

STATUS

editing

proposed

#11 by Jon E. Schoenfield at Tue Feb 19 04:07:10 EST 2019

NAME

Positive integers n k such that d(d(nk)) divides n, k, where d(nk) is the number of divisors of nk.

MAPLE

with(numtheory): a:=proc(n) if `mod`(n, tau(tau(n))) = 0 then n else end if end proc: seq(a(n), n=1..200); - _# _Emeric Deutsch_, Jun 05 2008

STATUS

approved

editing

#10 by Charles R Greathouse IV at Wed Apr 09 10:15:03 EDT 2014

AUTHOR

Leroy Quet , Jun 04 2008

Discussion

Wed Apr 09

10:15

OEIS Server: https://oeis.org/edit/global/2150

#9 by N. J. A. Sloane at Wed Feb 05 20:18:47 EST 2014

AUTHOR

_Leroy Quet _ Jun 04 2008

Discussion

Wed Feb 05

20:18

OEIS Server: https://oeis.org/edit/global/2118

#8 by Charles R Greathouse IV at Thu Nov 21 12:49:22 EST 2013

MATHEMATICA

Select[Range[200], Divisible[#, DivisorSigma[0, DivisorSigma[0, #]]]&] (* From _Harvey P. Dale, _, Feb 05 2012 *)

Discussion

Thu Nov 21

12:49

OEIS Server: https://oeis.org/edit/global/2062